DECOMPRESSION SICKNESS
DEFINITION
Decompression sickness (DCS) is a condition that occurs when divers come back to the surface too quickly after being deep under water. It is caused by the formation of nitrogen bubbles in the blood stream and, in the worst cases, can cause death.
DESCRIPTION
Decompression sickness is a relatively uncommon disorder among divers. Divers Alert Network (DAN), a worldwide organization devoted to safe-diving research and promotion, estimates that less than 1 percent of all divers experience the condition. A study conducted on Okinawa (an island in the Pacific Ocean near Japan) of military personnel who make tens of thousands of dives each year, found an average of one case of decompression sickness for every 7,400 divers and one death for every 76,900 dives. Mild cases may even go unnoticed by divers.
Decompression Sickness: Words to Know
- Decompression stops:
- Stops divers should make when returning to the surface to let the nitrogen in their blood dissolve safely out of their bodies. Charts developed by the U.S. Navy and other groups list the number of stops and the time to be spent at each stop.
- Hyperbaric chamber:
- A sealed compartment used to treat decompression sickness, in which pressure is first increased and then gradually decreased.
- Nitrogen:
- A tasteless, odorless gas that makes up four-fifths of Earth's atmosphere.
Decompression sickness is also known by other names, such as decompression illness and caisson (pronounced KAY-son) disease. DCS was called caisson disease in the nineteenth century because it occurred among construction workers who worked in caissons, building the supports for bridges at the bottom of lakes and rivers.
CAUSES
Air is primarily a mixture of two gases, oxygen and nitrogen. The oxygen we breathe in is used by cells in our bodies to metabolize (burn up) food. The nitrogen has no function in our bodies. Most of it is expelled from the body when we breathe out. Some of it is absorbed into our body tissues and our bloodstream.
As a person goes underwater, pressure increases on his or her body. The deeper one goes, the greater the pressure. This increased pressure forces more and more air into the body. All gases become more soluble (dissolve better) as pressure increases. Increased pressure causes no problem with oxygen, which is used up by the body. But it can cause problems with nitrogen. Deep under water, where the pressure is high, much more nitrogen dissolves in blood than it does at the surface.
Decompression sickness occurs when a person returns to the surface after being deep under water. When that happens, pressure on the person's body decreases. Nitrogen begins to come back out of the blood. If the person comes to the surface slowly, there is no problem. The nitrogen gas can escape from the blood slowly and be exhaled.
If the person comes up too quickly, however, a problem can develop. Nitrogen begins to form tiny bubbles as it escapes from the blood. The bubbles cannot be exhaled through the lungs. Instead, they can block blood vessels, push on nerves, and cause other disturbances in the body.
The amount of risk for DCS depends on the depth to which a person has gone under water. The deeper the dive, the greater the risk. To avoid decompression problems, divers may need to stop one or more times on their way back to the surface. Charts developed by the U.S. Navy and other groups list the number of stops and the time to be spent at each stop. When these directions are followed, nitrogen has time to escape from the bloodstream normally. Bubbles do not form, and DCS does not occur.
A number of factors can increase the risk of DCS for divers. For example, people who are overweight or who have recently had alcohol to drink are at greater risk for DCS. Also, people planning to fly or travel to high-altitude locations after diving are at increased risk for DCS because they experience further decompression at higher altitudes. Experts recommend that individuals wait between twelve to twenty-four hours after a dive before flying or traveling to high altitudes.
SYMPTOMS
Nitrogen bubbles can affect any of the body's tissues, including nerves, bone, blood, and muscles. For that reason, DCS can cause a wide variety of symptoms. These symptoms usually appear almost as soon as the diver surfaces. In 80 percent of all cases, they do so within eight hours of the dive.
The most common symptom of DCS is pain, often referred to by the term "bends." This pain can range from mild to severe. It usually affects the joints, but can occur anywhere. Skin problems, such as itching and rashes, are other symptoms. In more serious cases, DCS can result in paralysis, brain damage, heart attacks, and death.
DIAGNOSIS
Decompression sickness is usually first diagnosed by observing the diver's symptoms. If further care is necessary, a doctor may conduct a physical examination and take a medical history.
TREATMENT
Treatment of DCS involves reversing the conditions under which it first occurred. A person is placed into a hyperbaric (high pressure) chamber. Pressure is increased in the chamber, causing nitrogen gas bubbles to go back
into the bloodstream. The pressure in the chamber is then reduced slowly. Nitrogen gas escapes from the blood again, but not in the form of bubbles.
This treatment should be used even when a person's symptoms seem to have disappeared. Nitrogen bubbles may still be present in the blood, and symptoms may reappear at a later time.
Hyperbaric chambers are now available in many locations. DAN maintains a list of such facilities and provides a twenty-four-hour hotline that provides advice on DCS and other diving emergencies.
PROGNOSIS
DCS patients who receive treatment in a hyperbaric chamber usually experience a full recovery quickly. If treatment is delayed, the prognosis is less predictable. People who have been treated even a few days later, however, may still receive benefits. A 1992 report from DAN said that half of all divers who were treated immediately after an incident experienced full recovery. Others, however, experienced numbness, tingling, and other symptoms for a few weeks, months, or even a lifetime.
PREVENTION
Decompression sickness is an entirely preventable condition. Divers who follow rules of safe diving are unlikely to experience its effects. People who are overweight, have lung or heart problems, or are otherwise in poor health should not dive. Good divers should be aware of the need for decompression stops after a dive and follow standards developed for these stops.
FOR MORE INFORMATION
Books
Martin, Lawrence. Scuba Diving Explained: Questions and Answers on Physiology and Medical Aspects of Scuba Diving. Flagstaff, AZ: Best Publishing, 1997. [Online] http://www.mtsinai.org/pulmonary/books/scuba/welcome.htm (accessed May 22, 1998).
Periodicals
Clenney, Timothy L., and Lorenz F. Lassen, "Recreational Scuba Diving Injuries." American Family Physician (April 1996): pp. 1761+.
Organizations
American College of Hyperbaric Medicine. P.O. Box 25914–130, Houston, TX 77265. (713) 528–5931. http://www.hyperbaricmedicine.org.
Divers Alert Network (DAN). The Peter B. Bennett Center, 6 West Colony Place, Durham, NC 27705. (919) 684–8111; (919) 684–4326 (diving emergencies); (919) 684–2948 (general information). http://www.dan.ycg.org.
Undersea and Hyperbaric Medical Society. 10531 Metropolitan Avenue, Kensington, MD 20895. (301) 942–2980. http://www.uhms.org.